Jussi Putaala

Detection of Thermal Cycling-Induced Failures in RF/Microwave BGA Assemblies

The purpose of this paper was to investigate the effect of thermal cycling on the high-frequency behavior of ball grid array (BGA) interconnection structures. In order to characterize the applicability of RF measurements in predicting interconnection breakdown, a broadband BGA transition structure between a radio frequency printed wiring board (RF-PWB) and a ceramic module was fabricated. In addition to basic assemblies consisting of two BGA transitions between the module and substrate, the designed transition was applied in a passband filter module to demonstrate the effect of thermal cycling on the performance of a practical device, as well. The BGA test modules mounted on the PWBs were exposed to thermal cycling testing over a temperature range of -40degC to + 125degC. To detect interconnection failures induced by cyclic thermal stresses, both dc resistance and scattering parameter measurements were performed on the test assemblies at specific intervals. Parallel to the electrical measurements, crack propagation in the vicinity of the BGA transition structure was investigated using scanning acoustic microscopy (SAM). Moreover, scanning electron microscopy (SEM) was used to determine the failure mechanisms of the test assemblies. Degradation of the signal transmission characteristics of the basic assemblies was first observed at higher microwave frequencies as an increase in signal return loss (|S11|) and/or a change in its phase. The effect of TCT on the filter assembly was more constant and clearer to observe in the phase than in the magnitude of S11 in the passband. The dc resistance measurements showed no indication of degradation in any of the tested assemblies.

Reliability of ICA attachment of SMDs on inkjet-printed substrates

Abstract Printable electronics has been attracting considerable attention in recent years as a technology for flexible production of low-cost electrical devices on flexible substrates. Due to the additive nature of the production process, printable electronics offers to be a simple and effective method to manufacture electronics. Because the complexity and functionality of all-printed electrical devices is highly limited mainly by the low performance of semiconductive inks, external components are necessary for complex functionalities required in today’s electrical devices. Such components must be attached to printed structures with connections having adequate electrical and mechanical performance and good long-term reliability. This study evaluated the reliability of isotropically conductive adhesive connections on inkjet-printed substrates and viewed ICA component connections as viable options for attaching SMD components on inkjet-printed circuits.

Failure Detection of BGA Transition Structures at High Frequencies

The purpose of this paper was to investigate the effect of thermal cycling on the high frequency behavior of a BGA transition structure. A broadband microwave BGA transition structure between a RF-PWB and a ceramic module was designed and fabricated. The stand-off height of the composite BGA solder joints was 500 mum. The BGA test modules mounted on the PWBs were exposed to thermal cycling testing over a temperature range of -40...+125 degC. To detect interconnection failures induced by cyclic thermal stresses, both DC resistance and scattering parameter measurements (45 MHz-25 GHz) were performed on the test assemblies at specific intervals. Parallel to the electrical measurements, crack propagation in the vicinity of the BGA transition structure was investigated using scanning acoustic microscopy (SAM). Moreover, scanning electron microscopy (SEM) was used to determine the failure mechanisms of the test assemblies. Degradation in the signal transmission characteristics was first observed at higher microwave frequencies as an increase in signal return loss (|S11|). As the thermal cycling test proceeded, the reflected signal loss became more significant and gradually became pronounced at lower microwave frequencies. Pure DC resistance measurements showed no indication on the degradation of the transition structure

Enhanced thermal fatigue endurance and lifetime prediction of lead‐free LGA joints in LTCC modules

Purpose – The purpose of this paper is to describe the effect of indium alloying on the thermal fatigue endurance of Sn3.8Ag0.7Cu solder in low‐temperature co‐fired ceramic (LTCC) modules with land grid array (LGA) joints and the feasibility of using a recalibrated Engelmaier model to predict the lifetime of LGA joints as determined with a test assembly.Design/methodology/approach – Test assemblies were fabricated and exposed to a temperature cycling test over a temperature range of −40‐125°C. Organic printed wiring board (PWB) material with a low coefficient of thermal expansion was used to reduce the global thermal mismatch of the assembly. The characteristic lifetime, θ, of the test assemblies was determined using direct current resistance measurements. The metallurgy and failure mechanisms of the interconnections were verified using scanning acoustic microscopy, an optical microscope with polarized light, and scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) investigations. Lifetim...

A prognostic method for the embedded failure monitoring of solder interconnections with 1149.4 test bus architecture

This paper describes the feasibility of accurate low frequency measurements in predicting the breakdown of modern lead free ball grid array (BGA) interconnections. In these measurements, performed partly with 1149.4 analogue boundary scan, ceramic BGA modules measuring 15x15mm in width, with 9x9 ball matrixes, were attached on an FR-4 printed wiring board (PWB) and thermally cycled over a temperature range of -40 to +125^oC. The condition of corner interconnections was monitored using the developed measurement methods and construction. In-situ measurements were performed with a datalogger during temperature cycling, accompanied with 1149.4 mixed-signal test bus measurements of corner interconnections performed between cycling intervals. In addition, the measurements were complemented by scanning acoustic microscopy and, X-ray. Monitoring corner interconnections by a simple, low-frequency voltage measurement method with embedded test constructions gives an early warning indication well before the electrical interconnection failures. Of two studied interconnection compositions, the ones with plastic core solder balls (PCSB) proved to be more reliable than the ones with 90/10 PbSn balls.

Lifetime Prediction of Non-Collapsible Solder Joints in LTCC/PWB Assemblies Using a Recalibrated Engelmaier's Model

The thermal fatigue endurances of lead-free (φ 500 and 1100 μm) plastic core solder ball (PCSB) ball grid array interconnections were investigated. The test assemblies were exposed to thermal cycling testing in temperature ranges of 0-100°C and -40 to +125°C. In addition, optical microscopy and scanning electron microscopy were used to characterize the interconnections. The characteristic lifetime data from this and earlier studies were contrasted with a recalibrated Engelmaiers model. After adjusting the model, feasibility was determined through test results of a partial array representing a real-use case. On the basis of this paper it was found that the recalibrated Engelmaiers model is, after adjustment, a suitable model for predicting the lifetime of PCSB assemblies.

Failure mode characterization in inkjet-printed cpw lines utilizing a high-frequency network analyzer and post-processed tdr analysis

Failure mode characterization was applied to coplanar transmission lines by utilizing 0.5{10-GHz S-parameter measurements and post-calculated TDR (Time-Domain-Re∞ectometry) analysis. Coplanar waveguide transmission lines were inkjet-printed on 1.0-mm- thick ∞exible plastic RF substrates. Inductive, resistive, and capacitive types of failures | as the main failure modes caused by manufacturing, bending, or thermal cycling stresses | were investigated. The inkjet- printed CPW (Co-Planar Waveguide) lines were damaged by inductive shorts due to mechanical hitsor resistive and capacitive failures due to bending of the substrate. By using the TDR method the type and physical location of the failure can be determined.

Multilayer low-temperature co-fired ceramic systems incorporating a thick-film printing process

Abstract: Since the first application of low-temperature co-fired ceramics (LTCC) – a radar chip manufactured by DuPont and Hughes – in the 1980s, LTCC has gone through many changes, evolving from a simple multilayer substrate technology to a complex microelectronic system suitable for ‘intelligent’ packages with buried passive components, heat sinks, sensors, actuators, energy harvesters and even microsystems. Moreover, novel materials and enhanced processes have been introduced constantly. This chapter presents LTCC technology, starting from material development followed by processing steps and proposed applications. Future trends and challenges are discussed, and literature containing more detailed descriptions is listed.

Lifetime prediction and design aspects of reliable lead-free non-collapsible BGA joints in LTCC packages for RF/microwave telecommunication applications

Purpose – The purpose of this paper is to describe the behavior of different lead-free solders (95.5Sn3.8Ag0.7Cu, i.e. SAC387 and Sn7In4.1Ag0.5Cu, i.e. SAC-In) in thermomechanically loaded non-collapsible ball grid array (BGA) joints of a low-temperature co-fired ceramic (LTCC) module. The validity of a modified Engelmaier’s model was tested to verify its capability to predict the characteristic lifetime of an LTCC module assembly implementable in field applications. Design/methodology/approach – Five printed wiring board (PWB) assemblies, each carrying eight LTCC modules, were fabricated and exposed to a temperature cycling test over a −40 to 125°C temperature range to determine the characteristic lifetimes of interconnections in the LTCC module/PWB assemblies. The failure mechanisms of the test assemblies were verified using scanning acoustic microscopy, scanning electron microscopy (SEM) and field emission SEM investigation. A stress-dependent Engelmaier’s model, adjusted for plastic-core solder ball (...

Capability Assessment of Inkjet Printing for Reliable RFID Applications

In this paper, inkjet-printed silver traces and interconnections produced with the print-on-slope technique were used in an radio-frequency identification (RFID) structure operating in the ultra-high-frequency range. Underfill material was used to attach silicon RFID chips onto flexible, 125-